Hybrid Functional Polymer-Enabled Multiplexed Chemosensor Patch for Wearable Adrenocortex Stress Profiling.

Measuring bioactive stress hormones, including cortisol and dehydroepiandrosterone (DHEA), allows for evaluating the hypothalamic-pituitary-adrenal (HPA) axis functioning, offering valuable insights into an individual's stress response through adrenocortex stress profiles (ASPs). Conventional methods for detecting steroid hormones involve sample collections and competitive immunoassays, which suffer from drawbacks such as time-consuming labeling and binding procedures, reliance on unstable biological receptors, and the need for sophisticated instruments. Here, we report a label-free and external redox reagent-free amperometric assay directly detecting sweat cortisol and DHEA levels on the skin. The approach utilizes multitarget sensors based on redox-active molecularly imprinted polymers (redox MIPs) capable of selectively binding cortisol and DHEA, inducing changes in electrochemical redox features. The redox MIP consists of imprinted cavities for specific capture of cortisol or DHEA in a poly(pyrrole-co-(dimethylamino)pyrrole) copolymer containing hydrophobic moieties to enhance affinity toward steroid hormones. The polymer matrix also incorporates covalently linked interpenetrating redox-active polyvinylferrocene, offering a stable electrochemical redox feature that enables sensitive current change in response to the target capture in the vicinity. The multiplexed sensor detects cortisol and DHEA within 5 min, with detection limits of 115 and 390 pM, respectively. Through the integration of redox MIP sensors into a wireless wearable sensing system, we successfully achieved ambulatory detection of these two steroid hormones in sweat directly on the skin. The new sensing method facilitates rapid, robust determination of the cortisol-DHEA ratio, providing a promising avenue for point-of-care assessment of an individual's physiological state.

Enzyme-Mimics for Sensitive and Selective Steroid Metabolite Detection.

We present an enzyme-like functional polymer that recognizes nonelectroactive targets and catalyzes their redox reactions for simple, selective steroid metabolite detection. Measuring steroid metabolites, such as cortisol, has been widely adopted to diagnose stress and chronic diseases. Conventional detection method based on competitive immunoassay requires time-consuming labeling processes for signal transduction and unstable biological receptors for biorecognition yet with limited selectivity. Inspired by natural enzymes' target specificity and catalytic nature, we report an enzyme-mimic using electrocatalytic molecularly imprinted polymers (EC-MIP) to achieve label-free, external redox reagent-free, sensitive, and selective electrochemical detection of cortisol. The EC-MIP sensor contains molecularly imprinted cavities for specific cortisol binding and embedded copper phthalocyanine tetrasulfonate (CuPcTS) for electrocatalytic reduction of the ketones on the captured cortisol into alcohols. The direct sensing approach resolves the intrinsic limitations of conventional MIP-based sensors, most notably the use of external redox probes and weak sensing signals. The sensor exhibited a detection limit of 181 pM with significantly enhanced selectivity using a differential sensing mechanism. The new enzyme-like sensor can be modified to detect other targets, offering a simple, robust approach to future health monitoring technologies.

Reconfigurable photoinduced terahertz wave modulation using hybrid metal-silicon metasurface.

We present a photoinduced reconfigurable metasurface to enable high spatial resolution terahertz (THz) wave modulation. Conventional photoinduced THz wave modulation uses optically induced conductive patterns on a semiconductor substrate to create programmable passive THz devices. The technique, albeit versatile and straightforward, suffers from limited performance resulting from the severe lateral diffusion of the photogenerated carriers that undermines the spatial resolution and conductivity contrast of the photoinduced conductive patterns. The proposed metasurface overcomes the limitation using a metal-jointed silicon mesa array with subwavelength-scaled dimensions on an insulator substrate. The structure physically restrains the lateral diffusion of the photogenerated carriers while ensuring the electrical conductivity between the silicon mesas , which is essential for THz wave modulation. The metasurface creates high-definition photoconductive patterns with dimensions smaller than the diffusion length of photogenerated carriers. The metasurface provides a modulation depth of -20 to -10 dB for the THz waves between 0.2 to 1.2 THz and supports a THz bandpass filter with a tunable central frequency. The new, to the best of our knowledge, design concept will benefit the implementation of reconfigurable THz devices.

Nano gold-doped molecularly imprinted electrochemical sensor for rapid and ultrasensitive cortisol detection.

Rapid and sensitive detection of steroid hormone cortisol can benefit the diagnosis of diseases related to adrenal gland disorders and chronic stress. We report a molecularly imprinted polymer (MIP)-based electrochemical sensor that utilized nano gold-doped poly o-phenylenediamine (poly-o-PD) film to selectively determine trace level cortisol with enhanced sensitivity. The sensor detected cortisol levels by measuring the current change of the redox-active probes in response to the binding of target cortisol to the imprinted sites in the polymer. The gold-doped MIP (Au@MIP) sensor was prepared using a facile one-step in situ gold reduction and electropolymerization method to distribute high-density gold nanoparticles in the vicinity of the binding cavities. The in situ gold reduction promote the polymerization reaction, enlarging the effective surface area of the sensor. The nano gold doping also facilitated charge transfer when exposed to redox reagents. It enabled efficient blocking of the charge transfer upon the occupation of the cavities by cortisol, resulting in enhanced detection response and sensitivity. The Au@MIP sensor exhibited a high affinity toward cortisol binding with a dissociation constant Kd of ∼0.47 nM, a linear detection range from 1 pM to 500 nM with a detection limit of ∼200 fM, and satisfied specificity over other steroid hormones with highly similar structures. The sensor was successfully demonstrated to determine cortisol levels in spiked saliva in normal and elevated ranges. The facile antibody-free cortisol detection method was proved to be highly sensitive and selective, suitable for point-of-care testing applications.

Ferrocene-Grafted Carbon Nanotubes for Sensitive Non-Enzymatic Electrochemical Detection of Hydrogen Peroxide.

Sensitive detection of hydrogen peroxide (H2O2) residue in aseptic packaging at point of use is critical to food safety. We present a sensitive non-enzymatic, amperometric H2O2 sensor based on ferrocene-functionalized multi-walled carbon nanotubes (MWCNT-FeC) and facile screen-printed carbon electrodes (SPCEs). The sensor utilizes the covalently grafted ferrocene as an effective redox mediator and the MWCNT networks to provide a large active surface area for efficient electrocatalytic reactions. The electrocatalytic MWCNT-FeC modified electrodes feature a high-efficiency electron transfer and a high electrocatalytic activity towards H2O2 reduction at a low potential of -0.15 V vs. Ag/AgCl. The decreased operating potential improves the selectivity by inherently eliminating the cross-reactivity with other electroactive interferents, such as dopamine, glucose, and ascorbic acid. The sensor exhibits a wide linear detection range from 1 µM to 1 mM with a detection limit of 0.49 µM (S/N=3). The covalently functionalized electrodes offered highly reproducible and reliable detection, providing a robust property for continuous, real-time H2O2 monitoring. Furthermore, the proposed sensor was successfully employed to determine H2O2 levels in spiked packaged milk and apple juice with satisfactory recoveries (94.33-97.62%). The MWCNT-FeC modified SPCEs offered a facile, cost-effective method for highly sensitive and selective point-of-use detection of H2O2.

Colorimetric Urinalysis for On-Site Detection of Metabolic Biomarkers.

Over the past few decades, colorimetric assays have been developed for cost-effective and rapid on-site urinalysis. Most of these assays were employed for detection of biomarkers such as glucose, uric acid, ions, and albumin that are abundant in urine at micromolar to millimolar levels. In contrast, direct assaying of urinary biomarkers such as glycated proteins, low-molecular-weight reactive oxygen species, and nucleic acids that are present at significantly lower levels (nanomolar to picomolar) remain challenging due to the interferences from the urine sample matrix. State-of-the-art assays for detection of trace amounts of urinary biomarkers typically utilize time-consuming and equipment-dependent sample pretreatment or clean-up protocols prior to assaying, which limits their applicability for on-site analysis. Herein, we report a colorimetric assay for on-site detection of trace amount of generic biomarkers in urine without involving tedious sample pretreatment protocols. The detection strategy is based on monitoring the changes in optical properties of poly(3-(4-methyl-3'-thienyloxy)propyltriethylammonium bromide) upon interacting with an aptamer or a peptide nucleic acid in the presence and absence of target biomarkers of relevance for the diagnosis of metabolic complications and diabetes. As a proof of concept, this study demonstrates facile assaying of advanced glycation end products, 8-hydroxy-2'-deoxyguanosine and hepatitis B virus DNA in urine samples at clinically relevant concentrations, with limits of detection of ∼850 pM, ∼650 pM, and ∼ 1 nM, respectively. These analytes represent three distinct classes of biomarkers: (i) glycated proteins, (ii) low-molecular-weight reactive oxygen species, and (iii) nucleic acids. Hence, the proposed methodology is applicable for rapid detection of generic biomarkers in urine, without involving sophisticated equipment and skilled personnel, thereby enabling on-site urinalysis. At the end of the contribution, we discuss the opportunity to translate the homogeneous assay into a paper-based format.

Label-Free Sensitive Detection of Steroid Hormone Cortisol Based on Target-Induced Fluorescence Quenching of Quantum Dots.

We discovered that several types of steroid hormones quench the fluorescence of quantum dots (QDs) at close proximity. Inspired by the finding, we developed a new type of biosensor for the sensitive detection of cortisol via direct fluorescence quenching of functionalized QD probes directly induced by the capture of target cortisol without additional reporter reagents. The detection selectivity was provided by cortisol-selective aptamers or anticortisol antibodies conjugated on the QD surfaces. With the magnetic nanoparticle labeling, the new sensing method enabled rapid cortisol sensing at physiologically relevant concentrations and yielded the detection limit of ∼1 nM for aptamer-based sensors and ∼100 pM for antibody-based sensors. We also evaluated the new detection method using saliva samples with an optimized sample preparation process under the assistance of magnetic manipulation. The result showed a satisfying recovery rate for spiked saliva tests. The facile sensing technology offers an appealing approach for the detection of steroid hormones in point-of-care settings.

Flow-through colorimetric assay for detection of nucleic acids in plasma.

A flow-through colorimetric assay for detection of nucleic acids in plasma is reported. The proposed assay features an array of four polyvinylidene fluoride (PVDF) membranes impregnated with cationic poly (3-alkoxy-4-methylthiophene) (PT) as an optical reporter. The sensing strategy is based on monitoring the changes in optical properties of PT, upon complexation with target nucleic acids in the presence and in the absence of their corresponding complementary peptide nucleic acids (PNAs). As a proof of concept, the proposed methodology is validated using two biomarkers; lung cancer associated microRNA (mir21) and hepatitis B virus DNA (HBV-DNA). The flow-through colorimetric assay enabled detection of mir21 and HBV-DNA in plasma without requiring tedious sample pre-treatment and clean up protocols. Colorimetric responses for mir21 and HBV-DNA were obtained at nanomolar concentrations over five orders of magnitudes (from 1 nM to 10 µM), with a limit of detection of ∼0.6 nM and ∼2 nM in DI water and plasma, respectively. A logic gate system was developed to utilize the colorimetric assay responses as inputs for discrimination of mir21 and HBV-DNA and subsequently to obtain a profile of nucleic acids in samples that exceed respective clinical threshold limits, thereby enabling rapid and point of care (POC) disease diagnosis. Furthermore, the proposed methodology can be utilized for detection of a large number of nucleic acids in plasma by extending the array of PT impregnated membranes incorporated with their corresponding complementary PNAs.